The goal of this study is to examine the role that agrin plays in the formation of synapses in the central nervous system (CNS). Agrin is an extracellular protein that has been shown to induce postsynaptic differentiation at the developing neuromuscular junction (NMJ). Although agrin is known to be present in the CNS, no function for it has yet been described. At the NMJ agrin is a member of a complex of proteins that is associated with the cytoskeletal protein dystrophin. Duchenne muscular dystrophy (DMD) is caused by a genetic mutation in dystrophin, and mutations in other members of this complex lead to other forms of muscular dystrophy. Along with the devastating neuromuscular defects of DMD, cognitive deficits are also routinely reported. In order to further understand the process of synapse formation between two neurons, agrin binding to neurons and it's effect on synaptogenesis will be examined in a well defined cell culture system by the combination of immunohistochemical, biochemical and cell biological techniques. The specific Aims are: 1. To characterize the binding of alternatively spliced agrin isoforms to cultured rat hippocampal neurons. 2. To determine the co-localization of isoform-selective agrin binding sites with developing synapses and components of the DAPC in cultured hippocampal neurons. 3. To characterize novel b-dystroglycan-like proteins in the CNS.